diff --git a/tests/kded/serializertest.cpp b/tests/kded/serializertest.cpp
--- a/tests/kded/serializertest.cpp
+++ b/tests/kded/serializertest.cpp
@@ -124,6 +124,7 @@
 
     auto screen = config->screen();
     QCOMPARE(screen->currentSize(), QSize(1920, 1280));
+    QCOMPARE(Serializer::configId(config), QLatin1String("229fa9e8a378cb151d7302df42666774"));
 }
 
 void TestSerializer::testTwoScreenConfig()
@@ -154,6 +155,17 @@
 
     auto screen = config->screen();
     QCOMPARE(screen->currentSize(), QSize(3200, 1280));
+
+    auto configId = QLatin1String("8684e883209d7644eb76feea2081c431");
+    QCOMPARE(Serializer::configId(config), configId);
+
+    // make sure output IDs do not influence configId
+    OutputList reversed;
+    reversed[4] = config->output(2);
+    config->output(2)->setId(4);
+    reversed[2] = config->output(1);
+    config->setOutputs(reversed);
+    QCOMPARE(Serializer::configId(config), configId);
 }
 
 void TestSerializer::testRotatedScreenConfig()
@@ -184,6 +196,9 @@
 
     auto screen = config->screen();
     QCOMPARE(screen->currentSize(), QSize(2944, 1280));
+
+    auto configId = QLatin1String("8684e883209d7644eb76feea2081c431");
+    QCOMPARE(Serializer::configId(config), configId);
 }
 
 void TestSerializer::testDisabledScreenConfig()